1. Field of the Invention
The present invention relates generally to the field of medical diagnostics, and particularly to the field of determining physiologic characteristics of body lumens. In one particular aspect, the invention provides methods and apparatus for measuring the length of vascular lesions.
To properly treat many bodily diseases or abnormalities, certain physiologic characteristics, such as the size of a particular body member, often need to be determined. One example is in the treatment of vascular lesions, and particularly vascular aneurysms, which often requires the endoluminal placement of tubular prostheses, such as grafts, stents, and other structures. Before the prosthesis is placed in the vascular anatomy, the size of the lesion is measured so that a properly sized prosthesis can be selected.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending distally into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is by-passed and repaired with an artificial vascular graft. Recently, methods for endovascular graft placement for the treatment of aneurysms have been proposed. One such method and apparatus for endovascular placement of intraluminal prostheses, including both grafts and stents, is described in co-pending U.S. patent application Ser. No. 08/290,021, filed Aug. 12, 1994, the disclosure of which is herein incorporated by reference. A suitable intraluminal prosthesis for such a method includes a radially compressible, tubular frame having a proximal end, a distal end, and an axial lumen therebetween. The prosthesis is delivered to the area of interest via a delivery catheter. The prosthesis is then partially released from the catheter into a blood vessel or other body lumen to allow the prosthesis to radially expand and conform to the interior surface of the lumen being treated. The prosthesis can then be repositioned by the catheter until it is properly placed within the vessel. Other exemplary graft prostheses are described in co-pending U.S. patent application Ser. No. 08/255,681, the disclosure of which is herein incorporated by reference.
As previously described, before the endoluminal placement of an intraluminal prosthesis, it is desirable to first determine the appropriate size for the prosthesis so that the prosthesis will properly fit within the body lumen. For instance, in the case of vascular aneurysms, it is desirable to determine the length of the aneurysm so that the prosthesis will be long enough to extend through the diseased area of the vessel. In this way, both ends of the prosthesis can be attached to a healthy vessel wall. Current methods for determining the length of an effected body lumen employ fluoroscopy. To determine the length of a vessel using fluoroscopy, a catheter is inserted into the vessel and a contrast agent is injected into the vessel through the catheter. The blood flow carries the contrast agent along the vessel so that the vessel can be radiographically imaged with a fluoroscope. The fluoroscope produces a planar (or two dimensional) image of the vessel which can be evaluated to determine the existence of a diseased or abnormal area within the vessel. The length of the diseased or abnormal area is then estimated by measuring the length of the diseased area on the radiographic image. However, the length of such a measurement is typically not particularly accurate since it relies on discerning an ill-defined boundary in a single plane. Such a measurement does not take into account that the vessel is usually not in the same plane as the resulting fluoroscopic image. Hence, measurement of the body lumen using only a two-dimensional image can produce a length that is significantly less than the actual length of the body lumen. Another drawback to using such procedures to determine the length of a vessel is that the vessel is often non-linear, i.e. does not extend in a straight line. Hence, even if the vessel were in the same plane as the resulting fluoroscopic image of the vessel, it would still be difficult to measure the length of a curving vessel.
Improper determination of the vessel size can result in the selection of a prosthesis that is too short and hence cannot be properly grafted. The endoluminal placement of an improperly sized prosthesis can present a number of serious problems. One problem is that the prosthesis must be removed from the body lumen and replaced with another that is properly sized. This can often be difficult if the prosthesis has been radially expanded while in the body lumen. To remove the expanded prosthesis, the prosthesis must be radially compressed and then withdrawn from the body lumen. Such a procedure increases the risk of injury to the patient as well as unduly increasing operating time and expense.
Methods and apparatus are therefore needed for accurately measuring the length of a body lumen, and in particular the length of a vascular lesion. In one particular aspect, it would be desirable to provide improved methods and apparatus for the measurement of vascular aneurysms so that the proper size of intraluminal prostheses, such as grafts and stents, can be accurately determined. It would be further desirable if such methods and apparatus were simple to use and could be used with existing fluoroscopy technology.
2. Description of the Background Art
As previously described, methods and apparatus for placement and repositioning of intraluminal prostheses are described in U.S. patent application Ser. No. 08/290,021, the disclosure of which has previously been incorporated by reference. Suitable graft structures for placement in body lumens are described in U.S. patent application Ser. No. 08/255,681, the disclosure of which has previously been incorporated herein by reference.
U.S. Pat. No. 5,275,169 describes methods and apparatus for determining the internal cross-sectional area and diameter of a vessel.